1. Field of the Invention
The present invention is related to optical collimators and methods for making them, and more particularly to optical collimators assembled by means of gluing and welding.
2. Description of the Prior Art
An optical collimator with a Graded Index (GRIN) lens is used for collimating scattered light emitting from an output end of an optical fiber. The collimated light may then be efficiently and controllably utilized for transmission or testing.
As shown in FIG. 1, a conventional optical collimator 100 comprises an optical fiber 110, a ceramic ferrule 120, a GRIN lens 130 and an outer glass tube 140. The ferrule 120 has an inner end 122, an outer end 124, and a through hole 126 defined between the inner and outer ends 122, 124. A diameter of the through hole 126 is slightly greater than a diameter of the optical fiber 110. A cone-shaped opening (not labeled) is defined in the outer end 124, in communication with the through hole 126. The optical fiber 110 is typically sealed in the through hole 126 with UV-cured epoxy and 353-ND epoxy. To improve optical performance, the inner end 122 of the ferrule 120 and an inner end 112 of the optical fiber 110 are ground and polished to an oblique angle relative to an imaginary line that is perpendicular to respective longitudinal axes of the ferrule 120 and the optical fiber 110. The angle is typically between 6 and 8 degrees. The GRIN lens 130 has an inner end 132 and an outer end 134. The inner end 132 of the GRIN lens 130 is adjacent the inner end 122 of the ferrule 120, and is obliquely ground and polished to be parallel to the inner end 122. The longitudinal axis of the GRIN lens 130 is aligned with the longitudinal axis of the optical fiber 110. The ferrule 120 and the GRIN lens 130 are positioned and aligned in the glass tube 140, so that output light from the GRIN lens 130 can be accurately focused on the inner end 112 of the optical fiber 110. The ferrule 120 and the GRIN lens 130 are then fixed in place in the glass tube 140 with UV-cured epoxy and 353-ND epoxy.
When the optical fiber 110 is epoxied to the ferrule 120, and when the GRIN lens 130 and the ferrule 120 are epoxied to the glass tube 140, excess epoxy may contaminate the inner ends 112, 132 of the optical fiber 110 and GRIN lens 130. Such contamination reduces the output of the optical fiber 110, and diminishes the performance of the GRIN lens 130. The optical collimator 100 is prone to have large insertion loss. In addition, such contamination is difficult to remove. Furthermore, it is difficult to readjust the relative positions of the optical fiber 110 and the GRIN lens 130 after they have been secured in position. Moreover, typical epoxies need baking to be cured. These epoxies have a coefficient of thermal expansion several times larger than that of the GRIN lens 130. During baking of the epoxy, the accurate relative positions of the optical fiber 110 and the GRIN lens 130 are frequently altered. Accurate focusing of light from the GRIN lens 130 to the optical fiber 110 is accordingly diminished.
An improved optical collimator is needed to overcome the above-described numerous disadvantages of conventional optical collimators.
Accordingly, an object of the present invention is to provide an inexpensive optical collimator having low insertion loss.
Another object of the present invention is to provide an optical collimator free from contamination caused by excess glue.
A further object of the present invention is to provide an optical collimator which allows easy and precise adjustment of components thereof.
To solve the problems of the prior art and achieve the objects set out above, an optical collimator of the present invention comprises an optical fiber, a ferrule, a GRIN lens, a metal sleeve and an outer metal tube. The optical fiber has an exposed end which is inserted into the ferrule and glued thereinto. The GRIN lens is glued into the sleeve. Opposite ends of the GRIN lens protrude from opposite ends of the sleeve. The outer tube includes first and second receiving portions. The ferrule is glued into the first receiving portion, and the sleeve is secured in the second receiving portion. A plurality of soldering holes is defined in a periphery of the outer tube. Solder is applied to the sleeve through the holes to firmly connect the outer tube and the sleeve together. After assembly, if a position of the GRIN lens relative to the optical fiber is found to be inaccurate, the sleeve can be easily readjusted and re-soldered.
Other objects, advantages and novel features of the present invention will be apparent from the following detailed description of a preferred embodiment thereof with reference to the attached drawings, in which: